1. Field of the Invention
The present invention relates generally to the field of padlocks, and more specifically to a torque-resistant protective case enclosing a lock and a shackle.
2. Prior Art
While padlocks generally provide a measure of security for articles being protected, they have not been a completely effective deterrent in outdoor areas prone to vandalism or in areas requiring higher security against that kind of destructive activity. In most applications, a common padlock is vulnerable to cutting tools that can cut the shackle or to other tools, such as a pipe wrench, that can break the shackle, hasp or lock through torque. Historically, the shackle has been the most vulnerable portion of the padlock.
A development towards protecting the shackle was seen in U.S. Pat. No. 3,835,675 issued to Lippisch. Lippisch extended the encasing portion of the lock to cover a portion of the shackle. However, this design still left the shackles partially exposed and accessible to cutting tools. Thus, this device provided only a small amount of additional security over existing technology.
Further technical advances came when the entire lock and shackle were enclosed in a cylindrical casing. The casing caused the shackle to be covered when the lock was in use and attempted to prevent access to the protected object via cutting the shackle. Several fully encased padlocks are known in prior art. These generally include a hard, fixed casing that completely covers the shackle and are described in U.S. Pat. No. 6,338,261(Liu) and U.S. Pat. No. 5,345,794 (Jenks), incorporated herein by reference.
These designs solved the security problem that was caused by partially exposed shackles. However, because the design of the padlock called for the casing to be rigidly affixed to the lock, it left the lock, hasp or shackle vulnerable to attack by the application of torque, through a pipe wrench or other similar instrument. Thus, the new lock design fully enclosing the shackles was only marginally effective in deterring vandalism.
In further developments, guards and encasements were added to negate the torquing problem. The “guard approach” generally involved a guard that covered the approach to the lock, but was not integrated into the lock encasement (U.S. Pat. No. 5,172,574 to Perfetto and U.S. Pat. No. 5,469,722 to Ellefsen). A rotating encasement approach is exemplified in U.S. Pat. No. 3,820,360 (Best) or U.S. Pat. No. 5,669,255 (Albano), showing a freely rotating encasement. This approach addressed the torquing problem, but left the lock subject to vandalism because the rotating encasement could be easily rotated to a position where the keyhole was covered and then the encasement affixed to that position. Additionally, the freely rotating design often left the keyhole and the encasement hole misaligned, causing an inconvenience to the lock user.
However, none of the prior art has resolved the problem of protecting the hasp, which is the weakest part of the lock protection. The problem with breaking the hasp to gain entry into a locked object is that 1) unauthorized entry is allowed and 2) the process damages the thing to be protected. Thus, as vending machines become more expensive, it becomes increasingly important to protect them from damage through unauthorized entry.
Therefore, what has been needed is a padlock that is resistant to cutting, resistant to the application of torque and easy to install and use.